An electric power converter is an apparatus which converts electric power from one form into another form. Classes of electric power converters include AC-to-DC converters, AC-to-AC converters, DC-to-AC converters, and DC-to-DC converters. A conventional DC-to-DC converter comprises an inductor interposed between an input supply and an output, and a switching device which is controlled by a pulse-width modulator. The switching device alternately causes energy from the input supply to be stored in the inductor, and energy stored in the inductor to be provided to the output. By varying the duty cycle of the pulse-width modulator, the voltage at the output of the converter can also be varied. The location of the switching device within the converter is dependent upon the specific configuration employed, e.g. a buck converter configuration or a boost converter configuration.
In a conventional buck converter configuration, current passing through the inductor to the output causes an electromagnetic force on the inductor when the switching device is on. When the switching device is turned off, the electromagnetic force collapses, inducing a flyback current which flows to the output through a commutating diode. This configuration is disadvantageous in that its resulting efficiency is reduced by the conduction loss due to the commutating diode.
U.S. Pat. No. 5,072,171 to Eng discloses an improved switching converter which employs a synchronized switching system. This system includes a main switch, a commutation switch, and a Schottky flyback diode. The main switch and the commutation switch are controlled by a digital logic circuit in dependence upon a pulse width modulated signal. A preset delay signal is employed in the digital logic circuit in order to prevent simultaneous conduction of the two switches between the time at which the commutation switch is turned off and the time at which the main switch is turned on. FIG. 1 illustrates the resulting current flow through the main switch, the commutation switch, and the Schottky diode as a function of time. Since conduction loss in the commutation switch is less than in the Schottky diode, the resulting efficiency is improved as the conduction period through the Schottky diode is reduced. However, the current flow through the Schottky diode during the preset delay period degrades the efficiency of the converter.